1. Field of the Invention
This invention relates to an adhesive base material which contains a crosslinked polymer obtained by the polymerization of specific monomers, exhibits excellent adhesion to the skin, and is useful as plasters, medical pads, dermatologic medicines and the like.
2. Description of the Related Art
Known adhesive products for use in a form applied to the skin include those obtained by depositing a hydrophilic adhesive gel on a commercially-available support (Japanese Patents Laid-Open Nos. 111918/1987, 225314/1988, 246323/1988, etc.). Examples of support used in the above adhesive products include plastic sheets made of polyethylene, polypropylene, an ethylene-vinyl acetate copolymer, vinylon, a polyester, a polyurethane or nylon; nonwoven fabrics made of rayon or a polyester; and woven fabrics made of a polyester, an acrylic resin, silk or cotton. These supports are however accompanied with the problems that among them, the plastic sheets tend to peel off owing to the inferior adhesion with gel while the nonwoven and woven fabrics have poor flexibility and insufficient contraction.
As an adhesive base material to be impregnated with a water-soluble medicament, a water-soluble polymer or a water-soluble polymer having a crosslinked gel structure is used. Usable examples include polyacrylic acid, polyacrylate salts, polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethylcellulose sodium, gelatin and starch. Among them, the polyacrylic acid and polyacrylate salts are used by converting them into gels crosslinked with a multi-valent metal salt prior to their impregnation with a medicament (Japanese Patent Laid-Open No. 15413/1978). The crosslinked gels so obtained are however accompanied with the problem that they occur as heterogeneous gels because of unduly rapid crosslinking reactions.
With a view to overcoming such problems, it has been attempted to use a sparingly water-soluble multi-valent metal salt to retard the reaction velocity (Japanese Patent Laid-Open No. 42617/1982). This attempt is however accompanied with the problems that it causes excessive retardation of the reaction, and that when the amount of the multivalent metal salt is increased to accelerate the reaction velocity, the swelling property of the gel is reduced, thereby deteriorating the absorption of the medicament.
It has therefore been attempted to add a metal sequestering agent such as ethylene diamine tetraacetic acid (EDTA), citric acid, lactic acid or the like to increase the crosslinking reaction velocity of a sparingly water-soluble multivalent metal salt (Japanese Patents Laid-Open Nos. 106598/1979, 11614/1984, 110617/1984, etc.). This attempt is however accompanied with the problems that because of insufficient sequestering of the multivalent metal ions, the crosslinking reaction velocity does not show a marked increase and moreover the swelling property of the gel is reduced by unsequestered multivalent metal ions.
Known adhesive products impregnated with a sparingly water-soluble medicament include those obtained by impregnating an acrylic adhesive with indomethacin and a chemical enhancer (Japanese Patent Publications Nos. 43368/1983 and 7688/1984). The medicament has such a small solubility in the adhesive that the adhesive base material cannot be impregnated with a clinically required amount of the medicament. With a view to overcoming that problem, it has been attempted to use a copolymer composed of a monomer having an intramolecular acid-amide bond and a (meth)acrylate ester (Japanese Patent Laid-Open No. 138426/1983); or to co-pulverize a water-soluble polymer and a sparingly water-soluble medicament, followed by mixing with a carboxyvinyl polymer, a basic substance and water (Japanese Patent Laid-Open No. 135924/1991). Such attempts are however not fully satisfactory from the viewpoint of controllability of the solubility of the medicament, the crosslinking reaction velocity, the swelling degree and the like.